Steam boiler equipped with cooling device

ABSTRACT

The steam boiler has a circulation system for boiler water that has water pipes arranged to circulate boiler water and steam through the water pipes with a cooled device arranged to cool a selected, exposed part of the steam boiler. The cooled device has an outer tube and an inner tube arranged in the outer tube. The outer tube, at an upper end thereof, has an open connection to one of the water pipes in which water pipe a flow is established.

TECHNICAL AREA

The present invention concerns a steam boiler with a circulation system for boiler water that preferably has natural circulation.

BACKGROUND TO THE INVENTION

In steam boilers in which combustible material is combusted in a furnace, hot flue gases are formed that are conducted out of the steam boiler while the hot flue gases emit thermal energy to the boiler water circulating in a circulation system for the boiler. A prior art method of transferring thermal energy from hot flue gases to boiler water in a small steam boiler of an older type involves using a Field's steam boiler system from the late 19^(th) century in this steam boiler. To increase the heating area, vertical tubes (Field's tubes), closed at the lower ends, are used in this. They are suspended from the furnace roof. Inside these tubes are inner circulation tubes which are open at both ends. When the boiler is in operation, heat applied to the outer gap between the concentrically arranged tubes will achieve a steam/water mixture that has a lower density than the water in the inner tube. This creates natural circulation in these tubes which effectively increases the heat-absorbing area in the boiler. Heat is thus supplied to the stationary water volume above the sheet metal roof of the furnace from these Field's tubes. Despite early implementation, this application of Field's tubes has only been used to extend the heating area of a stationary, static volume of liquid to which heat is to be supplied. These Field's tubes are freely exposed in the furnace.

Regardless of how the heat is transferred to the boiler water, the flue gases, on their way out of the steam boiler, are conducted through ducts in which parts of the boiler are subject to extreme stress. If, for example, the steam boiler contains a cyclone for the separation of particles from the hot flue gases, the cyclone normally has an outlet tube which is extremely exposed to the hot flue gases. To allow it to last longer, it has been proposed, for example in U.S. Pat. No. 4,913,711, that the outlet tube can be cooled with cooling water fed using a pump to piping that leads to the outlet tube. A major disadvantage in this case is that a pump is required to cool this component. Another disadvantage is that the connection tube passes through the cyclone volume, thus disturbing the cyclone effect. This connection tube must be well protected against erosion.

There are also examples of cooled outlet tubes embodied by vertical water-bearing tubes next to each other. These tubes receive their water from below. One disadvantage of this is that these supply tubes are long and subject to severe erosion and may disturb the operation of the cyclone.

It is easy to see that, in a steam boiler, not only the outlet tube of a cyclone may be subject to stress on account of heat but that the high temperature may also constitute a problem for the material in the walls and other components in the entire steam boiler. The aim of the present invention is to offer an improved steam boiler in which various exposed parts of the steam boiler can become more durable by being cooled effectively.

DESCRIPTION OF THE INVENTION

The present invention concerns a steam boiler with a circulation system for boiler water that preferably has natural circulation. The circulation system comprises water pipes arranged in such a way that, when the steam boiler is in operation, they can circulate boiler water through the pipes in a circuit in which water passes from the steam dome in the outer down tube to the furnace and convection parts and in which water and steam pass from the furnace and convection parts up to a steam dome in which steam is separated from the circuit.

The steam boiler comprises a device designed to cool a selected, exposed part of the steam boiler. The cooled device comprises an outer tube and an inner tube placed in the outer tube. The outer tube has an upper end with an open connection to one of the water pipes for boiler water and a sealed lower end. The inner tube has an upper open end connected to a water pipe for boiler water and a lower open end at the outer tube's sealed lower end. In some embodiments, the inner tube's upper open end is located at the outer tube's upper end and they are connected to the same water pipe or flow for boiler water. The cooled device extends at least partially in a vertical direction downwards from the point at which the outer tube is connected to a water pipe.

The steam boiler may comprise an element that is exposed to hot gases when the steam boiler is used. The element that is exposed to hot gases when the steam boiler is used may consist of a wall in the steam boiler or a holder for the heat exchanger in the path of the flue gas or the cooled device may be arranged in or in fact constitute this wall or holder.

The element that is exposed to hot gases when the steam boiler is used may also consist of, for example, a thermocouple or a through tube that extends through the pipe for boiler water and through the inner tube of the cooled device and, at its very end, connects to the outer tube of the cooled device.

The steam boiler may comprise a cyclone for separation of particles from hot flue gases, in which connection the cyclone has an outlet tube for the hot gases. In such case, the cooled device may be arranged to create a cooled outlet tube.

The cyclone's outlet tube may be constructed of or comprise a number of cooled devices, each of which cooled devices comprises an outer tube and an inner tube arranged in the outer tube, which outer tube, at an upper end, has an open connection to one of the pipes for boiler water and a sealed lower end and the inner tube has an upper end at the outer tube's upper end and a lower open end at the outer tube's sealed lower end and the cooled device may extend at least partially in a vertical direction downwards from the point at which the outer tube is connected to the water pipe.

In some embodiments, at least some of the pipes for boiler water may be inside the cyclone's walls and extend in a vertical direction from a lower part of the cyclone to a higher part of the cyclone. Some of the pipes for boiler water that extend inside the cyclone's walls may, in such case, be connected to cooled devices provided with an outer and an inner tube.

According to one embodiment, the steam boiler may have walls that form a flue gas duct in which one or more elements are suspended by means of a holder, which holder comprises a cooled device in accordance with the present invention, i.e. a cooled device with an outer tube and an inner tube arranged in the outer tube, which outer tube, at an upper end, has an open connection to one of the water pipes for boiler water and a sealed lower end, in which connection the inner tube has an upper open end at the outer tube's upper end and a lower open end at the outer tube's sealed lower end and the cooled device extends at least partially in a vertical direction downwards from the point at which the outer tube is connected to the water pipe.

According to another embodiment, a flue gas duct formed from the walls of the steam boiler may comprise a separating partition wall that separates two parts of the flue gas duct from each other. In such case, the partition wall may be at least partially constructed of cooled devices in accordance with the present invention, i.e. cooled devices comprising an outer tube and an inner tube arranged in the outer tube, which outer tube, at an upper end, has an open connection to one of the water pipes for boiler water and a sealed lower end, in which connection the inner tube has an upper open end at the outer tube's upper end and a lower open end at the outer tube's sealed lower end and the cooled device extends at least partially in a vertical direction downwards from the point at which the outer tube is connected to the water pipe.

According to another embodiment, the cooled device is used as a dust-separating beam in a flue gas duct formed from the walls of the steam boiler. In such case, a number of cooled devices may be placed next to each other in the flue gas duct. When the cooled device is used as a dust-separating beam, the cooled device may be provided with outer rails that extend along the cooled devices.

The inner tube's upper end may be funnel-shaped.

The inner tube may, at its upper end, have a mouth that is at a slant to the inner tube's longitudinal axis.

The connection to the water pipe for boiler water may be in an area in which the lower side of the pipe for boiler water has been expanded to meet the outer tube.

At the upper end of the outer tube a lid may be arranged to cover part of the gap area between the outer and the inner tubes.

At its upper end, the inner tube may be inclined towards the wall of the outer tube.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows schematically a section of a steam boiler.

FIG. 2 shows in perspective and in section a cyclone for a steam boiler.

FIG. 3 shows a cooled device in accordance with the present invention.

FIG. 4 shows in perspective the construction of an outlet in a cyclone provided with cooled devices.

FIG. 5 is a side view of the upper part of the cyclone outlet shown in FIG. 4.

FIG. 6 is a top view of part of the cyclone outlet shown in FIG. 4.

FIG. 7 shows a section of a part in the lower part of FIG. 4.

FIG. 8 shows in section part of a cyclone with a cooled outlet tube.

FIG. 9 is a schematic side view of a sand seal between the cyclone and the furnace in a steam boiler.

FIG. 10 is an enlargement of part of FIG. 9 showing another embodiment of the cooled device.

FIG. 11 shows a section of an embodiment of the cooled device used in the invention.

FIG. 12 is a schematic side view of another embodiment.

FIGS. 13 a and 13 b show another embodiment seen in a side view and a top view.

FIG. 14 is a schematic side view of an embodiment in which one or more cooled devices are used as holders for one or more elements suspended in a flue gas duct.

FIG. 15 shows schematically how one or more cooled devices are used as a wall that supports elements.

FIG. 16 shows schematically how a partition wall may be arranged in a flue gas duct.

FIG. 17 shows in section a side view of an embodiment of the invention.

FIG. 18 shows a variant of the embodiment shown in FIG. 17.

FIGS. 19-30 show side views in section of various embodiments of the cooled device itself.

FIGS. 31 a-34 b show sections of further embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a steam boiler 1 that comprises a furnace 6 in which combustion takes place. The steam boiler 1 may, for example, be a CFB boiler (Circulating Fluidised Bed boiler) in which the combustion air is supplied at the base. The steam boiler 1 has a circulation system 2 for boiler water. The circulation system 2 comprises water pipes 3, 4 arranged in such a way that, when the steam boiler 1 is in operation, they can circulate boiler water through the pipes 3, 4 in a circuit in which water and steam pass from the furnace 6 up to a steam dome 5 in which steam is separated from the circuit and water runs back towards the furnace 6.

In FIG. 1, the reference number 3 indicates water pipes in which water and steam rise towards the steam dome 5, while the reference number 4 designates water pipes in which water runs down from the steam dome 5 towards the area of the furnace 6. The downward water pipes 4 may appropriately be arranged separate from the furnace 6, for example on the outside of the steam boiler 1, so that no heat is supplied to water running from the steam dome on its way down. Down in the area of the furnace 6, the water may then be used to absorb thermal energy and transfer the thermal energy to the steam dome. The circulation of the boiler water in the pipes is driven by the strong heat generated in the furnace 6. Low-density water mixed with steam rises in the pipes while water with a higher density from the steam dome 5 runs down.

FIG. 1 and FIG. 2 also show that the steam boiler 1 comprises a cyclone 7 that is used to separate ash and sand from the hot flue gases formed in the furnace 6. In the cyclone 7, the hot flue gases can pass out through the outlet tube 11 while sand and ash fall towards the lower part 9 of the cyclone 7. Combustible material that has not been fully combusted is also separated and can return to the furnace 6 via the lower part 9 of the cyclone 7. The hot flue gases in the cyclone 7 cause major stress, in particular to the outlet tube 11. Such outlet tubes 11 are normally made of fireproof sheet metal. However, the outlet tube is sensitive to hot gas corrosion, in particular in waste-fired boilers. It is also difficult to cope with expansion close to the suspension. The consequence is reduced durability, in some cases only 2-3 years. In addition to major costs for each replacement, the downtime itself also entails costs as a result of non-production. FIG. 1 and FIG. 2 also show how water pipes 3 for boiler water run inside the cyclone 7's walls 8 and from there to the steam dome 5.

Other parts of the steam boiler 1 are also exposed to stress by the hot gases.

A cooled device 12 will now be explained with reference to FIG. 3. The cooled device 12 is shown in FIG. 3 connected to a pipe 3 for flowing boiler water. The cooled device 12 comprises an outer tube 13 and an inner tube 14 arranged in the outer tube 13. The outer tube 13 has, at an upper end 15, an open connection to the water pipe 3 for boiler water and a sealed lower end 16. The inner tube 14 has an upper open end 17 that is also connected to a water pipe 3 and a lower open end 18 at the outer tube's sealed lower end 16. In the embodiment in accordance with FIG. 3, the inner tube 14's lower end 18 is arranged at the outer tube 13's sealed lower end 16 and both the outer tube 13 and the inner tube 14 are connected to the same water pipe 3 for boiler water. However, embodiments are conceivable in which the outer tube 13 and the inner tube 14 are connected to different pipes 3 for boiler water. The cooled device 12 extends at least partially in a vertical direction downwards from the point at which the outer tube 13 is connected to a water pipe 3. FIG. 1 shows how the water pipe 3 for boiler water runs horizontally. It is suitable for the cooled device 12 to be connected at a point where the water pipe 3 is horizontal but the water pipe 3 could also be inclined upwards in the direction of flow. The cooled device 12 works as follows. When the cooled device 12 extends downwards into an area with hot flue gases, water that is located in the gap between the outer tube 13 and the inner tube 14 will be mixed with steam and have a lower density than the water located inside the inner tube 14. The steam/water mixture therefore rises in the gap between the outer tube 13 and the inner tube 14. The water located inside the inner tube 14 has a higher density and will fall instead. Part of the boiler water that flows in pipe 3 will then be sucked down in the inner tube 14 and will subsequently return upwards, absorbing thermal energy from the area around the cooled device 12. The boiler water in the water pipe 3 flows from left to right in the figure, as shown by the arrows.

The normal water flow rate in the water pipe 3 is in the range 0.3 to 1.5 m/s. The water flow rate established in the downward tube 14 is 0.5 to 2.5 m/s and in the outer gap between tubes 13 and 14 it is 0.2 to 1.0 m/s.

In accordance with the present invention, a cooled device 12 is used that works according to the principle shown in FIG. 3 to cool a selected, exposed part of the steam boiler 1.

With reference to FIGS. 1-2 and 4-8, the steam boiler may comprise a cyclone 7 to separate solid particles such as ash, sand or fuel that was not combusted in the furnace from flue gases. Water pipes 3 pass the cyclone on their way up to the steam dome 5. FIG. 2 shows how water pipes 3 for boiler water extend in a vertical direction from a lower part 9 of the cyclone 7 to a higher part 10 of the cyclone 7. In accordance with one embodiment, the cyclone 7's outlet tube 11 may comprise at least one cooled device 12. As explained earlier in connection with FIG. 3, the cooled device 12 comprises an outer tube 13 and an inner tube 14 arranged in the outer tube 13. The outer tube 13 has, at an upper end 15, an open connection to a water pipe 3. In this case, the cooled device 12 may use the water in water pipe 3 to cool the outlet tube 11.

In an embodiment best shown in FIGS. 4-7, the outlet tube 11 consists of a number of the cooled devices 12, each of which comprises an outer tube 13 and an inner tube 14 arranged in the outer tube 13.

The water pipe 3 that is used is suitably one of the water pipes 3 that run inside the walls 8 of the cyclone 7. In practice, a number of such water pipes 3 pass through the cyclone 7 and meet higher up in the system. FIGS. 4 and 5 show how some water pipes 3 a continue directly upwards when they reach the area of the outlet tube 11, while other water pipes 3 b proceed to the cooled devices 12 that have an outer tube 13 and an inner tube 14, as shown in FIG. 3. In FIGS. 4 and 5, the inflow 3 in is established to the pipes 3 a, 3 b towards the tube ends that are in a horizontal plane, oriented in towards the centre of the cyclone, and the outflow 3 out is established in the tube ends that are vertically oriented in the figure. As a suggestion, every other water pipe 3 b may proceed to the cooled devices 12. In this case, the cooled devices 12 may be arranged side by side so that together they form an outlet tube 11 for hot flue gases, as shown in FIG. 4. How this embodiment works is shown best in FIG. 8. As shown in FIG. 8, the boiler water rises in water pipes 3 that run inside the walls of the cyclone 7. When the water reaches the area of the outlet tube 11, some of the boiler water will descend in the cooled devices 12 that form the outlet tube 11. This boiler water will move downwards in the inner tubes 14 of the cooled devices while the steam/water mixture will, on account of its lower density, move upwards in the outer gap between tube 13 and tube 14.

FIG. 8 also indicates how the cooled devices 12 are connected to each other, at their lower ends, via an annular tube 33.

The cooled device 12 may thus, in itself, form durable parts of the steam boiler 1 exposed to heat. Alternatively, the cooled device 12 may also be used to cool an element that, when the steam boiler 1 is used, is exposed to hot flue gases (directly or indirectly). Such an embodiment will now be explained with reference to FIG. 9 and FIG. 10. FIG. 9 shows a sand seal located in the lower part of the cyclone 7. The sand seal comprises a wall 19 that, when the steam boiler 1 is in operation, is exposed to major stress via strong heat. As shown in FIG. 10, a cooled device 12 in accordance with the present invention, is arranged inside the wall 19 in the part marked XIII in FIG. 9. The cooled device 12 in the sand seal's wall 19 is constructed in the same way as the cooled device 12 in FIG. 3 and it works in the same way. The cooled device 12 is connected to a pipe 3 for boiler water that rises inside the cyclone 7's walls 8 and part of this boiler water is therefore used to cool a wall 19 in the sand seal of the cyclone 7. After the cooled device 12, the water pipe 3 continues vertically upwards while the pipe up to the cooled device runs horizontally.

Another embodiment is shown in FIG. 11. In the embodiment shown in FIG. 11, a through tube 21 has been passed through the outer wall of the water pipe 3 and through the inner tube 14 of the cooled device 12. At its lower end, the through tube 21 connects to the outer tube 13 of the cooled device 12. The through tube 21 consists of an element that may be used to add an additive to the steam boiler or to suck out flue gases for sampling. Without the cooled device 12, the hot flue gases would act on this element unimpeded. The cooled device 12 can now cool the through tube and contribute to increasing its service life.

Another embodiment will now be explained with reference to FIG. 12 and FIG. 27. In embodiments with an inner through tube 21, a thermocouple 20 may be introduced via the through tube 21. In such case, the thermocouple is kept cooled using the cooled device 12.

Another embodiment will now be explained with reference to FIGS. 13 a and 13 b. FIG. 13 a shows how a number of dust separation beams were created by a number of cooled devices 12 being suspended as cooled separation beams in a flue gas duct. The cooled devices 12 may suitably be suspended in the flue gas duct 23 so that they form a thin row as shown in FIG. 13 b. The cooled devices 12 in FIG. 13 a are designed according to the same principle as shown in FIG. 3 with an outer tube 13 and an inner tube 14. A water pipe 3 for boiler water in which water flow is established is connected to the cooled devices in FIG. 13 a. As shown in FIG. 13 b, the cooled devices used as separation beams may be provided with outer rails 28 that extend along the cooling devices 12. The outer rails 28 contribute to intercepting particles, for example ash particles, which then fall.

Another embodiment is shown in FIG. 14. FIG. 14 shows how an element 24 in a flue gas duct 23 may be suspended in the flue gas duct 23 in a cooled device 12 which functions as a holder for this element. The element 24 may consist, for example, of a tube structure such as part of a superheater or economiser. The holder for the tube structure 24 is then cooled and is better able to resist heat stress.

Another embodiment is shown in FIG. 15. A separately fired superheater 35 is supported here by a wall created from cooled devices 12, each of which comprises an outer and an inner tube in accordance with the principle shown in FIG. 3. Of course, here too the cooled devices 12 are connected to a water pipe 3 for boiler water in which a water flow is established.

FIG. 16 shows an embodiment in which a number of cooled devices 12 form a partition wall in a flue gas duct, which partition wall separates one part of the flue gas duct 23 from another part. The partition wall here has an increased service life due to its ability to resist heat. Of course, these cooled devices 12 also have an outer and an inner tube in accordance with the principle shown in FIG. 3 and they are connected to a pipe 3 for boiler water.

FIG. 17 shows schematically how a number of cooled devices 12 may be connected to a water pipe 3, for example to form a row of separation beams in accordance with FIGS. 13 a and 13 b or a partition wall in accordance with FIG. 16.

FIG. 18 shows a variant of the arrangement shown in FIG. 17. FIG. 17 shows how the inner tube 14 in which water runs down is connected to a water pipe 3 other than the outer tube 13 in which a water/steam mixture with lower density moves upwards. The boiler water flows here in a first water pipe 3, descends via the inner tube 14, rises in the gap between tube 13 and tube 14 in one or more cooled devices 12 and flows out in a second water pipe 3.

A few more embodiments will now be explained with reference to FIGS. 19-21.

In conventional Field's boilers, the cooling tubes are designed to make it easier for the boiler water to be sucked down in the inner tube 14. Thus the inner tube 14 may, at its upper end 17, be shaped as a funnel 29 to reduce the pressure drop in this part and, to a certain extent, guide the rising steam/water mixture away from the inlet of the inner tube. This embodiment may also be applied when the cooled devices 12 are connected to a water pipe with boiler water in which a water flow is established.

In the embodiment in accordance with FIG. 20, the effect of the water flow is utilised in the tube 3. The inner tube 14 has here, at its upper end, been given a mouth that is at a slant to the tube's longitudinal axis. This is so that the water that, in FIG. 20, flows from left to right, finds it easier to flow into the inner tube 14 and establish a static pressure against the inlet of the inner tube.

In the embodiment in accordance with FIG. 21, the embodiment is adapted to an established water flow in the pipe 3 which may contain some steam. The cooled device 12's connection to the water pipe 3 has here been arranged in an area 31 of the water pipe 3 in which the lower side of the water pipe 3 has been expanded to meet the outer tube 13. This lower position is advantageous if the water pipe 3 contains a lot of steam.

Another aspect will now be explained with reference to FIGS. 22-25, in which the effect of the water flow in the tube 3 is used. In connection with a cooling device 12 that is connected to a water pipe 3, it is desirable for steam formed in the boiler water that has already passed through the outer tube 13 of the cooled device 12 not to be sucked back down in the inner tube 14.

FIG. 22 shows how a lid has been arranged at the upper end 15 of the outer tube to cover part of the gap area between the outer tube 13 and the inner tube 14. When the flow in the water pipe 3 goes from left to right in FIG. 22, the lid 32 prevents steam in the outer tube 13 from entering the water pipe 3 in this area. Steam goes instead out to the right in the figure, i.e. the steam continues in the water pipe. In the inner tube 14, boiler water that comes from the left in the figure under increased pressure via the inlet is instead sucked down. The lid also produces an ejector effect on the steam/water mixture that flows out from the outer tube as the flow rate increases in this area.

FIG. 23 shows a similar embodiment but the lid 32 is extended here. The idea here is that the water flow passing with a certain increased ejector effect will take the steam/water mixture leaving the cooled device 12 with it.

The embodiment in accordance with FIG. 24 shows how the inner tube 14, at its upper end, is inclined towards the wall of the outer tube 13. This also results in a reduced risk of steam being sucked into the inner tube 14.

The embodiment in accordance with FIG. 25 shows how the embodiment in accordance with FIG. 24 may be combined with the embodiment in accordance with FIG. 21.

FIG. 26 shows an embodiment that, in principle, is similar to the embodiment in accordance with FIG. 21. In addition, a through tube 21 has been added that can be used to suck out samples from the steam boiler or to add an additive.

FIG. 27 shows an embodiment that is similar to that in FIG. 26 but in which the through tube 21 has also been utilised to introduce a thermocouple 20.

FIG. 28 shows an embodiment that is similar to that in accordance with FIG. 27 but here a drainage tube 36 has also been added that can be used to drain the cooled device 12.

FIG. 29 shows an embodiment in which the inner tube 14 is arranged at the inner wall of the outer tube 13. This may also reduce the risk of steam being sucked down in the inner tube 14. The inner tube 14 may have a rear edge 37 at the side of the inner tube 14 that is downstream in the water pipe 3's direction of flow. The rear edge 37 that sticks up on the downstream side also contributes to reducing the risk of steam being sucked down in the inner tube 14.

In accordance with the embodiment shown in FIG. 30, the inner tube 14 has been split in two in its upper part. The reference number 38 refers to the holder for the inner tube 14.

FIGS. 31 a and 31 b show an embodiment in which the cooled devices 12 are arranged connected to a joint upper box 39 located at an angle in relation to the water pipe 3 for boiler water. The cooled devices 12 jointly form a wall that may, for example, be a partition wall. The cooled devices 12 may be connected to each other via the connection pieces 40, which may consist, for example, of welded-on sheet metal or flat steel.

FIGS. 32 a and 32 b show an embodiment equivalent to that in accordance with FIG. 31 a but in which the lower ends of the cooled devices 12 are also connected via a joint lower box 34 that also constitutes a joint lower closed end for the outer tubes 13.

FIGS. 33 a and 33 b show an embodiment that is, in principle, similar to that in FIG. 32 a. However, these figures also show a drainage tube 36 that has been passed down through an inner tube 14 in a cooling device 12.

FIGS. 34 a and 34 b show an embodiment that differs from the embodiment in accordance with FIG. 33 a in that the drainage tube 36 does not run through an inner tube 14. Instead one of the outer tubes in a row of the cooled devices only contains a drainage tube. The flow of water down in the cooled devices 12 takes place here in the inner tubes 14 in the other cooled devices.

The embodiments shown in the figures may be used in steam boilers of different types and, in principle, everywhere there is a heated space or a part that is exposed to heating and where there is also a flow of water in a pipe that passes the area or the part that needs to be cooled.

The invention offers a simple method for cooling parts that are exposed to strong heat. When the invention is applied to the outlet tube in a cyclone, it offers the advantage that the existing flow of boiler water can be used and no separate pipe is required into the cyclone from outside with the additional complications this entails. In addition, no separate pump for the flow of cooling water is required. 

1. A steam boiler, comprising: a furnace; a circulation system for boiler water, the circulation system having a water pipe connected thereto and adapted to circulate boiler water and steam through the water pipe in a circuit; the circulation system being in operative engagement with the furnace; a cooled device in operative engagement with the water pipe, the cooled device having an outer tube and an inner tube arranged in the outer tube, the outer tube, at an upper end thereof, having an open connection defined therein connected to the water pipe; the outer tube having a sealed lower end; the inner tube having an upper open end connected to the water pipe and a lower open end at the sealed lower end; and the cooled device extending at least partially in a vertical direction downwardly from the upper end of the outer tube.
 2. The steam boiler according to claim 1 wherein the cooled device is in operative engagement with an element to cool the element.
 3. The steam boiler according to claim 2 wherein the element consists of a wall in the steam boiler and the cooled device is arranged inside the wall.
 4. The steam boiler according to claim 2 wherein the element consists of a thermocouple.
 5. The steam boiler according to claim 2 wherein the element consists of a through tube that extends through the water pipe and through the inner tube and connects to the outer tube.
 6. The steam boiler according to claim 1 wherein the steam boiler comprises a cyclone for separating ash from hot flue gases, the cyclone has an outlet tube for the hot flue gases and the cooled device is arranged to cool the outlet tube.
 7. The steam boiler according to claim 6 wherein the outlet tube consists of a number of cooled devices each cooled device comprises an outer tube and an inner tube.
 8. The steam boiler according to claim 6 wherein the steam boiler has a plurality of water pipes and at least some of the water pipes are inside walls of the cyclone and extend in a vertical direction from a lower part of the cyclone to a higher part of the cyclone and some of the water pipes which extend inside the walls of the cyclone are connected to the cooled devices by the outer tube and the inner tube.
 9. The steam boiler according to claim 1 wherein the steam boiler has walls that form a flue gas duct and the cooled device constitutes a holder for an element that is suspended in the flue gas duct.
 10. The steam boiler according to claim 1 wherein the steam boiler has walls that form a flue gas duct and the cooled device, together with a number of similar cooled devices, form a partition wall that separates two parts of a flue gas duct from each other.
 11. The steam boiler according to claim 1 wherein the steam boiler has walls that form a flue gas duct and the cooled device is arranged in the flue gas duct as a separation beam and is provided with outer rails.
 12. The steam boiler according to claim 1 wherein the upper open end of the inner tube is funnel-shaped.
 13. The steam boiler according to claim 1 wherein the inner tube, at the upper end thereof, has a mouth that is at a slant to a longitudinal axis of the inner tube.
 14. The steam boiler according to claim 1 wherein an area is disposed at a lower side of the water pipe that has been expanded to meet the outer tube.
 15. The steam boiler according to claim 1 wherein a lid is arranged at the upper end of the outer tube to cover part of a gap area between the outer tube and the inner tube.
 16. The steam boiler according to claim 1 wherein the inner tube, at an upper end thereof, is inclined towards a wall of the outer tube. 